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Concrete repairs

Queensway shops are situated in a residential area of Gainsborough.  The shops are located on the ground floor, with direct public access, whilst above the shops there are residential flats on the second and third floors.

A report had been received by the housing association, responsible for the maintenance of the block, that a section of concrete had fallen from the roof canopy and this posed a public safety hazard.

Topbond were asked to investigate the cause and extent of the damage visible on the soffit of the cantilever roof canopy, which ran the full length of the shopping parade. The report was to incorporate a suitable remedial specification.

Topbond undertook some in-situ testing for depth of cover, half-cell potential and carbonation depth measurement as well as the collection of some dust samples for chloride analysis.  In addition a delamination survey was undertaken   The finding revealed areas of low cover to the soffit of the canopy, with depth of carbonation extending to the steel reinforcement.

Water was entering into the roof slab through failed areas of the asphalt surfacing which was then leaking out via joints in the canopy.

This had contributed to the onset of reinforcement corrosion.  Topbond proposed a patch repair scheme using a lightweight cementitious repair mortar and an anticarbonation coating, together with patch repairs to the areas of failed asphalt on the canopy.

The works had to be undertaken during the day and full public access had to be maintained to the busy shops during the repair phase.  Topbond’s PASMA trained staff erected mesh fence panels around the mobile scaffolding towers used to access the soffit. The defective concrete was broken out and the corroded steel reinforcement was cleaned and primed before the area was reinstated with repair mortar.  The asphalt defects were repaired by a specialist roofing contractor